1. Field of the Invention
The present invention relates to light-absorbing materials, and, more particularly, to materials, called optical limiters, that passively protect optically sensitive materials from overexposure to high intensity light.
2. Description of Related Art
Optically sensitive materials such as optical sensors and the human eye are used to detect light because they contain components which are sensitive to light energy. In one common example, an optoelectronic sensor, such as an "electric eye", produces a voltage when light falls upon a sensing material within the sensor. However, such sensors can be "blinded" by overexposure to high intensity light, just as the human eye becomes blinded if it is exposed to overly intense light. In each case, exposure to high intensity light can temporarily or even permanently destroy the ability of the optically sensitive material to react to light.
There are two approaches to protecting such optically sensitive materials against blinding by overexposure to high intensity light. In the first, or "active" approach, when the electronic circuitry of the optically sensitive device detects a harmfully high intensity of light, it operates a mechanism to interpose a physical barrier between the light source and the optically sensitive material. The second, or "passive" approach, is employed when the onset of the harmful high-intensity light is so fast that no active system has the time to respond. In a passive protection system, a barrier is formed directly in response to the incident light. Such systems are called "optical limiters" and are characterized by the behavior that as the intensity of incident light increases, the intensity of light transmitted through the system also increases up to a saturation level. Above the saturation level, the transmitted light intensity remains substantially constant even with increasing intensity of incident light.
Organometallic compounds and some organics have been observed to show optical limiting characteristics, but all of the compounds suffer from at least one of the following: high optical intensity thresholds for optical limiting, undesirable manufacturing properties, or not effective over a broad band of optical radiation.
A desirable optical limiter would have a low optical intensity threshold for optical limiting, would be easy to manufacture, could be utilized in device manufacture, and would be effective over a reasonably broad bandwidth.